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Introduction to drug classification

Learning objectives for this chapter

By the end of this chapter, we would like you to:

- Understand how and why drugs have chemical, generic and trade names and the implications of this.

- Understand how drugs are generally classified by their structure, or by their function (physiological or therapeutic effects) and be able to apply this understanding.

- Understand how prescribed drugs are regulated in the UK by law and by regulatory bodies such as the NMC.

- Appreciate how a good understanding of drug classification can enhance nursing practice and patient safety.

- Understand why some drugs are classified as requiring special care when prescribing, especially in specific patient populations such as pregnant or breastfeeding women.

Drug Naming

Drugs have a chemical name, a generic name and a trade name under which it is sold. To write these correctly, a drug's trade name is capitalised, however the generic and chemical names are not. One of the reasons why drugs may be sold under trade names rather than simply as generic preparations is that the cost of developing a drug, testing it through preclinical and clinical trials and bringing it to market is very expensive (Sertkaya et al., 2016, p.117). By protecting production of the drug for the first few years of its use, the company who developed the drug can recoup the development cost by selling the drug under a trade name. After this time, other companies can make the drug (under other trade names or as a generic copy), allowing the drug to be available at a lower price. This ensures that the need for the pharmaceutical company to receive the financial benefits of selling the drug is balanced with the need to control prices.

Drugs Are Classified by Their Chemical Family, Physiological or Therapeutic Effect

Medicinal drugs can firstly be classified into prescription drugs, or non-prescription drugs - commonly referred to as over the counter (OTC) drugs. OTC drugs can include remedies for common ailments, or drugs in a lower dosage than would be prescribed by a doctor or nurse practitioner (for example, paracetamol and ibuprofen). These are generally considered to be safe when used correctly and it is not usually necessary for their use to be monitored by healthcare professionals. On the other hand, prescription-only drugs are generally intended to treat more significant conditions, and legally require an appropriately qualified healthcare professional (for example, a doctor or nurse practitioner) to make a diagnostic decision, and then a decision about which drug is most suitable for use in that circumstance.

Drugs are generally classified by family or by the physiological effects they can cause. Table 1 shows the two ways that drugs can be described. The effects can either be physiological (i.e. its effects on the body's systems) or therapeutic (i.e. its medicinal use). For example, the drug citalopram could be described by its physiological effect as a selective serotonin-reuptake inhibitor (SSRI), or by its therapeutic action as an antidepressant. There is therefore often overlap between drug classification systems.

Drug classifications by family (or active ingredient)

Drug classification by physiological effect

Drug classification by therapeutic effect

ACE inhibitors




Selective serotonin-reuptake inhibitors (SSRIs)



CNS depressant





Heparin (and mimetics)



Table 1: Examples of drug classifications by family or active ingredient or by effect

In addition to this, there are also other classification systems in operation for specific uses, such as according to the relative safety of the drug in pregnant women, whether or not athletes would be permitted to compete while taking the drug, or whether prescription of a drug should be controlled to prevent harm or misuse.

The Nursing and Midwifery Council and Drugs

Incorrect administration of drugs may cause harm to patients, or even death. It is therefore essential that the administration of drugs is carefully regulated. In the UK, this is primarily carried out by government legislation and policy, however the professional bodies that represent each type of healthcare professional also have their own guidelines. For nurses, drug administration guidance is given by the NMC - specifically, the NMC Standards for Medicine Management (NMC, 2016). These guidelines not only describe safe and effective drug administration practice, but also encourage nurses to follow local and national policies for drug administration, as most institutions will have specific guidelines for their nurses to follow.

Controlled and Non-Controlled Drugs

All drugs can be classified as either controlled or non-controlled. Controlled drugs require additional care in their prescription and administration, as these drugs have the capability to either cause significant harm to patients if taken incorrectly, or have the potential to be abused. Harm can be characterised as physiological damage, mental harm, or causing psychological and physiological dependence. Dependence on the abuse of controlled drugs can also have many harmful effects on society. By implementing and enforcing procedures and policies to restrict the use of these drugs, the safety of patients, the public and healthcare professionals can be ensured. The guidelines for the use of controlled drugs cover every step of the drug's life - from its production to its storage, prescription, administration and even wastage if unused.

The Misuse of Drugs Act 1971 sub-classifies controlled drugs by their potential to cause harm when misused. As well as prescription drugs, this also includes drugs that do not have a medicinal use, such as lysergide (LSD). Harm can be caused by abuse of these medications in the form of addiction, and organisations such as The Royal College of General Practitioners (RCGP) recognise the responsibility of prescribers to consider this risk when prescribing these medications to patients (2013). However, it should be remembered that despite this, where a clinical need for a controlled drug is indicated, such as the use of morphine in the palliative care of cancer patients experiencing pain, it is not recommended by NICE to restrict the use of controlled drugs through fear of creating dependence. In this case, the risk of creating a dependence is considered to be far outweighed by the necessity of controlling the patient's pain.

Classification of drugs by potential risk to patient health

Most drugs are known to have potential adverse effects in patients, usually identified during the drug development and clinical trial stage, or in the UK, through the Yellow Card reporting system monitored by the Medicines and Healthcare Products Regulatory Agency (MHRA) (BNF, 2016b). These may include observed adverse effects, interactions with other drugs, vaccines or even complementary and herbal medicines. Adverse effects can be relatively minor or very severe. Furthermore, some drugs can themselves cause severe illness such as cardiac dysfunction. It is important that these risks are understood by prescribers, and a careful analysis should be undertaken of the potential cost to the patient of taking the drug in comparison with the potential benefits. If the patient is fully informed of the risks, and the healthcare team feel that the drug is still in the patient's best interest, then informed consent can be taken from the patient and the drug prescribed. A common example of this is the cytotoxic anticancer drug trastuzumab, which is associated with a significant risk of congestive heart failure (Popat and Smith, 2008, p.325). However, as trastuzumab has been shown to be an effective treatment for HER2 positive breast cancer, its use is still recommended, although careful patient monitoring and cessation of treatment in the event of cardiac toxicity is recommended by NICE (NICE, 2010). In order to manage the risk of cytotoxic drugs to patients, drugs classified as cytotoxic (i.e. that may cause harm to some systems as well as treating tumours) require special handling. For example, they should only be prepared by trained personnel in designated pharmacy areas. Healthcare professionals handling these drugs should wear protective clothing (gloves, masks and gowns), and local procedures for the control of spillages and disposal of waste should be followed (BNF, 2016a).

Drugs may also be classified by the potential risk they pose when administered during pregnancy. Some drugs, such as diethylstilboestrol (thalidomide), have the potential to cause congenital malformation (teratogenesis) when administered in the first trimester. Similarly, some can affect the development of the foetus or its growth, particularly when administered in the second and third trimesters, which may be linked with congenital abnormalities such as cleft palate, heart defects or low birth weight, although evidence for this link is mixed (Nezvalová-Henriksen et al., 2013). Although many drugs are considered to not be harmful in pregnancy, it is difficult to classify these medications as "safe", as ethical considerations prevent the use of clinical trials in pregnant women, therefore evidence tends to be based on reports of complications following usage. In general, prescribers are advised to only prescribe drugs when the benefits to the mother outweigh the potential risk to the foetus. This risk can be evaluated from evidence obtained from animal studies of teratogenicity, or evidence from studies or reported examples of teratogenicity in humans. Prescribers may also have similar concerns when prescribing to breastfeeding women, as there is a possibility that the drug may enter the breast milk and therefore be passed to the infant, however the potential risk of this is dependent on the pharmacokinetics of the drug (how it acts and is metabolised in the body), the rate of absorption and elimination of the drug by both mother and infant, and the potential effects of any drug (or drug metabolites) on the infant. In the UK, previously the BNF contained a table classifying the potential harmfulness of drugs during pregnancy, however in recent editions this has been replaced with recommendations for use in pregnant or breastfeeding women under each individual drug entry, with the general recommendation that drugs should only be prescribed to pregnant women if the benefit to the mother outweighs any potential risk. Institutions may have local recommendations for drug choices in pregnant women, or have produced their own formularies.

Implications of Drug Classification Systems for Nurses

It is important that nurses have a good understanding of the way in which drugs are named, as confusion between the names could cause medication errors which could affect patient safety, as some trade names are fairly similar. For example, the trade name of the antiepileptic drug lamotrigine is Lamictal, which is similar to the drug name Lamisil (generic name terbinafine), which is a topical antifungal agent. Nurses should therefore be familiar with both generic and trade names of drugs, and check any names they are unfamiliar with. As many prescriptions are handwritten, misspellings or unclear writing could cause similar trade names to be confused. However, it should be remembered that the nurse administering the medication has a legal and ethical responsibility to ensure that the right drug is administered, therefore the nurse is responsible for querying any unfamiliar or hard to read instructions. Finally, the nurse should consider any patient-specific risks to administering any prescribed medication, such as pregnancy, and should always check if there is any doubt that this has been considered. Although it may be difficult to question a prescribing doctor's decision owing to the historical imbalance between the professions, raising a question in a respectful and open manner should not be seen as a negative.


Drug classification is an important concept for nurses to be familiar with. This is so that you can understand the potential risks of any medications, and so that you can ensure that your patients have the necessary information to give informed consent for their treatment. By understanding how drugs are commonly named and classified, you should understand why it is advisable to use a drug's generic name rather than trade names where possible, and understand how confusion between trade names may cause prescribing errors. This should help you to identify prescribing errors in your future nursing practice, which will enhance the safety of your patients and the quality of care you can offer them. Finally, you should now be aware of why controlled drugs are classified as such, and why they should be treated differently to non-controlled drugs. You should also now understand that some patient populations are at particular risk from certain classifications of drug and be confident in advising them accordingly.

References list

BNF. (2016a). 8.1 Cytotoxic Drugs. NICE. [Online]. Available at: http://www.evidence.nhs.uk/formulary/bnf/current/8-malignant-disease-and-immunosuppression/81-cytotoxic-drugs [Accessed: 20 October 2016].

BNF. (2016b). Adverse Reactions to Drugs. BNF. [Online]. Available at: https://www.evidence.nhs.uk/formulary/bnf/current/guidance-on-prescribing/adverse-reactions-to-drugs [Accessed: 19 October 2016].

Nezvalová-Henriksen, K., Spigset, O. and Nordeng, H. (2013). Effects of ibuprofen, diclofenac, naproxen, and piroxicam on the course of pregnancy and pregnancy outcome: a prospective cohort study. BJOG, 120 (8), p.948-959.

NICE. (2010). Technology Appraisal Guidance TA208: Trastuzumab for The Treatment of HER2-Positive Metastatic Gastric Cancer. NICE. [Online]. Available at: https://www.nice.org.uk/guidance/ta208?unlid=72997535920169247211 [Accessed: 19 October 2016].

NMC. (2016). Standards for Medicines Management. Nursing and Midwifery Council. [Online]. Available at: http://www.nmc.org.uk/standards/additional-standards/standards-for-medicines-management/ [Accessed: 19 October 2016].

Popat, S. and Smith, I. E. (2008). Therapy insight: Anthracyclines and trastuzumab - the optimal management of cardiotoxic side effects. Nature Clinical Practice. Oncology, 5 (6), pp.324-335.

RCGP. (2013). RCGP Substance Misuse and Associated Health. RCGP. [Online]. Available at: http://www.smmgp.org.uk/download/guidance/guidance021.pdf [Accessed: 19 October 2016].

Sertkaya, A., Wong, H.-H., Jessup, A. and Beleche, T. (2016). Key cost drivers of pharmaceutical clinical trials in the United States. Clinical Trials, 13 (2), pp.117-126.